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PISIDIAD^. 263 
higher up the same river, on stones of a small over- 
fall at Tansor: he believes they were introduced 
from Wisbeach on timber since 1828. 
It has been naturalised in Holland and on the 
Rhine. It is also found with tertiary fossils in 
Transylvania, Moravia, and near Vienna. 
Mr. Lyell {GeoL), not being aware that these 
animals had the power of living a long time out of 
water, and that they were most probably brought in 
the holds of ships with the Baltic timber, and thus 
introduced into our docks, where the timber is un- 
loaded, believes that the animals attached themselves 
to the bottoms of Baltic ships, and in this manner 
were obliged to pass through the sea, before being 
again brought to their natural station in fresh water. 
And Mr. Garner, in his curious but rather crude 
paper on the anatomy of Lamellibranchiata (^Mag. 
Nat, Hist, n. s. hi. 303.), ventures to explain this 
theory by supposing that the animals kept their 
valves constantly closed ” during the voyage through 
the sea to the fresh water ! 
Order III. LASIACEA, 
Fam. 3. PISIDIADAE. 
Mantle lobes united; pedal and branchial opening 
inferior ; syphon conical, more or less elongate ; 
foot lanceolate, compressed, not byssiferous ; 
S 4 
